Build libcxx and libcxxabi via llvm-project/runtimes

This is the new method to build runtimes as of LLVM 12, and the previous
standalone method is deprecated since LLVM 14 and unsupported since
LLVM 15 (6f17768e11)

Building libcxx and libcxxabi in one go simplifies the setup necessary
as:
- tests CMakeLists.txt have some wrong dependencies which would need
  to be worked around.
- LIBCXXABI_LIBCXX_INCLUDES is not recognized when building separately
  and passing -I paths via the command line yields msys path munging
  problems on Windows.

This effectively drops support for LLVM 11 and older.

Makefile

@@ -126,7 +126,7 @@ build/compiler-rt.BUILT: build/llvm.BUILT build/wasi-libc.BUILT
 	cp -R $(ROOT_DIR)/build/llvm/lib/clang $(BUILD_PREFIX)/lib/
 	touch build/compiler-rt.BUILT
 
-# Flags for libcxx.
+# Flags for libcxx and libcxxabi.
 LIBCXX_CMAKE_FLAGS = \
     -DCMAKE_C_COMPILER_WORKS=ON \
     -DCMAKE_CXX_COMPILER_WORKS=ON \
@@ -136,11 +136,13 @@ LIBCXX_CMAKE_FLAGS = \
     -DCMAKE_STAGING_PREFIX=$(PREFIX)/share/wasi-sysroot \
     -DLLVM_CONFIG_PATH=$(ROOT_DIR)/build/llvm/bin/llvm-config \
     -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON \
+    -DCXX_SUPPORTS_CXX11=ON \
     -DLIBCXX_ENABLE_THREADS:BOOL=OFF \
     -DLIBCXX_HAS_PTHREAD_API:BOOL=OFF \
     -DLIBCXX_HAS_EXTERNAL_THREAD_API:BOOL=OFF \
     -DLIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY:BOOL=OFF \
     -DLIBCXX_HAS_WIN32_THREAD_API:BOOL=OFF \
+    -DLLVM_COMPILER_CHECKED=ON \
     -DCMAKE_BUILD_TYPE=RelWithDebugInfo \
     -DLIBCXX_ENABLE_SHARED:BOOL=OFF \
     -DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY:BOOL=OFF \
@@ -150,30 +152,6 @@ LIBCXX_CMAKE_FLAGS = \
     -DLIBCXX_CXX_ABI_INCLUDE_PATHS=$(LLVM_PROJ_DIR)/libcxxabi/include \
     -DLIBCXX_HAS_MUSL_LIBC:BOOL=ON \
     -DLIBCXX_ABI_VERSION=2 \
-    -DWASI_SDK_PREFIX=$(BUILD_PREFIX) \
-    --debug-trycompile
-
-build/libcxx.BUILT: build/llvm.BUILT build/compiler-rt.BUILT build/wasi-libc.BUILT
-	# Do the build.
-	mkdir -p build/libcxx
-	cd build/libcxx && cmake -G Ninja $(LIBCXX_CMAKE_FLAGS) \
-		-DCMAKE_SYSROOT=$(BUILD_PREFIX)/share/wasi-sysroot \
-		-DCMAKE_C_FLAGS="$(DEBUG_PREFIX_MAP)" \
-		-DCMAKE_CXX_FLAGS="$(DEBUG_PREFIX_MAP)" \
-		-DLIBCXX_LIBDIR_SUFFIX=$(ESCAPE_SLASH)/wasm32-wasi \
-		$(LLVM_PROJ_DIR)/libcxx
-	ninja $(NINJA_FLAGS) -C build/libcxx
-	# Do the install.
-	DESTDIR=$(DESTDIR) ninja $(NINJA_FLAGS) -C build/libcxx install
-	touch build/libcxx.BUILT
-
-# Flags for libcxxabi.
-LIBCXXABI_CMAKE_FLAGS = \
-    -DCMAKE_C_COMPILER_WORKS=ON \
-    -DCMAKE_CXX_COMPILER_WORKS=ON \
-    -DCMAKE_AR=$(BUILD_PREFIX)/bin/ar \
-    -DCMAKE_MODULE_PATH=$(ROOT_DIR)/cmake \
-    -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON \
     -DLIBCXXABI_ENABLE_EXCEPTIONS:BOOL=OFF \
     -DLIBCXXABI_ENABLE_SHARED:BOOL=OFF \
     -DLIBCXXABI_SILENT_TERMINATE:BOOL=ON \
@@ -183,31 +161,25 @@ LIBCXXABI_CMAKE_FLAGS = \
     -DLIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY:BOOL=OFF \
     -DLIBCXXABI_HAS_WIN32_THREAD_API:BOOL=OFF \
     -DLIBCXXABI_ENABLE_PIC:BOOL=OFF \
-    -DCXX_SUPPORTS_CXX11=ON \
-    -DLLVM_COMPILER_CHECKED=ON \
-    -DCMAKE_BUILD_TYPE=RelWithDebugInfo \
-    -DLIBCXXABI_LIBCXX_PATH=$(LLVM_PROJ_DIR)/libcxx \
-    -DLIBCXXABI_LIBCXX_INCLUDES=$(BUILD_PREFIX)/share/wasi-sysroot/include/c++/v1 \
-    -DLLVM_CONFIG_PATH=$(ROOT_DIR)/build/llvm/bin/llvm-config \
-    -DCMAKE_TOOLCHAIN_FILE=$(ROOT_DIR)/wasi-sdk.cmake \
-    -DCMAKE_STAGING_PREFIX=$(PREFIX)/share/wasi-sysroot \
     -DWASI_SDK_PREFIX=$(BUILD_PREFIX) \
     -DUNIX:BOOL=ON \
     --debug-trycompile
 
-build/libcxxabi.BUILT: build/libcxx.BUILT build/llvm.BUILT
+build/libcxx.BUILT: build/llvm.BUILT build/compiler-rt.BUILT build/wasi-libc.BUILT
 	# Do the build.
-	mkdir -p build/libcxxabi
-	cd build/libcxxabi && cmake -G Ninja $(LIBCXXABI_CMAKE_FLAGS) \
+	mkdir -p build/libcxx
+	cd build/libcxx && cmake -G Ninja $(LIBCXX_CMAKE_FLAGS) \
 		-DCMAKE_SYSROOT=$(BUILD_PREFIX)/share/wasi-sysroot \
 		-DCMAKE_C_FLAGS="$(DEBUG_PREFIX_MAP)" \
 		-DCMAKE_CXX_FLAGS="$(DEBUG_PREFIX_MAP)" \
+		-DLIBCXX_LIBDIR_SUFFIX=$(ESCAPE_SLASH)/wasm32-wasi \
 		-DLIBCXXABI_LIBDIR_SUFFIX=$(ESCAPE_SLASH)/wasm32-wasi \
-		$(LLVM_PROJ_DIR)/libcxxabi
-	ninja $(NINJA_FLAGS) -C build/libcxxabi
+		-DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
+		$(LLVM_PROJ_DIR)/runtimes
+	ninja $(NINJA_FLAGS) -C build/libcxx
 	# Do the install.
-	DESTDIR=$(DESTDIR) ninja $(NINJA_FLAGS) -C build/libcxxabi install
-	touch build/libcxxabi.BUILT
+	DESTDIR=$(DESTDIR) ninja $(NINJA_FLAGS) -C build/libcxx install
+	touch build/libcxx.BUILT
 
 build/config.BUILT:
 	mkdir -p $(BUILD_PREFIX)/share/misc
@@ -216,7 +188,7 @@ build/config.BUILT:
 	cp wasi-sdk.cmake $(BUILD_PREFIX)/share/cmake
 	touch build/config.BUILT
 
-build: build/llvm.BUILT build/wasi-libc.BUILT build/compiler-rt.BUILT build/libcxxabi.BUILT build/libcxx.BUILT build/config.BUILT
+build: build/llvm.BUILT build/wasi-libc.BUILT build/compiler-rt.BUILT build/libcxx.BUILT build/config.BUILT
 
 strip: build/llvm.BUILT
 	./strip_symbols.sh $(BUILD_PREFIX)